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Bryobia from Hedera, Apple and Pear (Acar., Tetran.) Notulae Ad Tetranychidas 1 by G

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Bryobia from Hedera, Apple and Pear (Acar., Tetran.) Notulae Ad Tetranychidas 1 by G 340 ENTOMOLOGISCHE BERICHTEN, DEEL 15, 1.IV. 1955 Bryobia from Hedera, apple and pear (Acar., Tetran.) Notulae ad Tetranychidas 1 by G. L. VAN EYNDHOVEN Introduction. In 1836 and 1838 the great arachnologist Carl Ludwig Koch published 4 species of mites for which he created the genus Bryobia, viz. B. praetiosa and gloriosa in 1836, B. speciosa and nobilis in 1838. Later, in the year 1842, he indicated B. speciosa as type of the genus Bryobia 1836, but our actual rules of nomenclature do not agree with this as the type of a genus has to be chosen out of those species which were published at the moment of the erection of the new genus in question. So actually Bryobia praetiosa C. L. Koch 1.1.1836 is considered as the typus generis. The next point is: What is Bryobia praetiosa ? This cannot be said with cer¬ tainty, as no specimens of Koch are known to be still available. The only details we dispose of, are a rather minute description and a coloured plate, very good for the moment of publication more than a century ago, but unsufficient for our requirements of to-day. It has been pretended that Koch separated his Bryobia-species by colour only, and that these colours would not be valuable for differentiation. By this pronoun¬ cement, however, one does a wrong to this arachnologist. Koch paid much at¬ tention to the characters of the living animal and he has recorded them in many cases so eminently that many recent acarologists may follow his example. But moreover Koch has given in text and plate, also for Bryobia, various morpho¬ logical differences which may be very valuable. So I am convinced that his B. speciosa is really a good species, though not the B. speciosa pictured by Berlesf (1888), which is quite another animal, and that also B. gloriosa is existing. The same conception has been published by A. C. Oudemans (1937) in his great work. Many Bryobia-specimens and eventually Bryobia-species have been found and mentioned since Koch’s days. Bryobia proved to occur on many host plants, dif¬ ferences were stated especially in biological sense, but no sufficiently fixed mor¬ phological characters were found to separate all these forms or (biological) races, and the tradition developed to consider them all as ”Bryobia praetiosaAll publications, especially those dealing with applied entomology, are struggling with this problem of identification. Oudemans (1927) has seen morphological differ¬ ences and has stated that it would be necessary to describe and draw the species very exactly, but he has never been able to work it out. It is not my intention to give a review of the numerous publications here. I hope to have an occasion later. For the moment I should like to refer to the review of Roosje & van Dinther (1953), which gives a recapitulation of the most important species and of the literature. For years already I knew this Bryobia-problem, and I had the impression that notwithstanding the great resemblance of specimens coming from different host plants it must be possible to separate them by morphological characters. This year BRYOBIA FROM HEDERA, APPLE AND PEAR 341 I have been able to make a start for studying by the support of the Laboratorium voor Entomologie, Wageningen, and the Nederlandse Organisatie Zuiver-Weten- schappelijk Onderzoek (Z.W.O.). After having compared material from various plants in the Netherlands and some other countries, I have come to the conclusion that it will be possible to give well defined morphologically separated characters of a certain number — if not all — of Bryobid-forms. On this principle I have based the 2 species described hereunder, one of them provisionally without a name owing to the confusion still existing in nomenclature of previous days. I fully realize that this effort to come to a morphological separation of the Bryobid-species will not be more than a first step. I dispose of various other, well defined forms, which will be published as soon as they have been studied suf¬ ficiently. It is not by accident that I have chosen for this first publication out of various well-defined forms those of apple/pear and of ivy (Hedera helix). These are 2 of the 3 forms that are the most important for practice. The third one is that of goose¬ berry (Ribes uva-crispa — grossuldrid), and this perhaps is the best known host plant for Bryobid, for here we find a real and regular pest expressed in names like ’’kruisbessenspint” (Netherlands) and ’’Stachelbeermilbe” (Germany). I am of opinion that the material I have seen so far, justifies to separate the three biological ’’races” morphologically. The gooseberry mite is not described here, as it still needs some further study in the coming spring, but the limited material I have seen shows very clear differences. If all gooseberry mites will prove to belong to one form, this will have a name already, viz. Bryobid ribis Thomas 1894. A typical, * secundary difficulty is that the individual specimens are varying rather heavily even in those characters which are of morphological value. Not¬ withstanding this, however, it is possible, after having seen a sufficient number of individuals, to separate them within rather sharp limits. I have considered at large whether it would be possible or even necessary to maintain the widely spread name "prdetiosd” for one of the three forms from apple/pear, ivy and gooseberry. I think this to be neither possible nor necessary. From the moment we start splitting up the species ”Bryobid prdetiosd”, and wish to maintain this name for one of the above forms, all forms but one will have to get another name. So there is no objection at all to give another name to dll of them. It is even not possible to chose this name ,,prdetiosd” for any of these three forms, for C. L. Koch gives the habitat in his original description of 1836 as follows: ”In Gärten, zuweilen auf Gesträuch. Bei Regensburg in den Bösner- garten, selten”. The indication ”in Gärten” may mean herbaceous plants. The „Gesträuch” cannot be apple or pear, nor Hederd, but it might have been Ribes uvd-crispd ( = grossuldrid). However, ’’zuweilen” means ’’sometimes”, so that this Ribes cannot be considered as the normal host plant for B. prdetiosd Koch (non auct.). Bryobid prdetiosd C. L. Koch 1.1.1836 sensu stricto must be a Bryobid living in gardens or parks at Regensburg, not available at present, but most probably morphologically differing from the 3 forms cited above. 342 ENTOMOLOGISCHE BERICHTEN, DEEL 15, 1.IV. 195 5 It would also not be possible to fix the name for one of the forms of these host plants by depositing a neotype, for the rules of nomenclature prescribe for this that the neotype corresponds as exactly as possible with the original description and is coming from the same geographic region. So first of all it would be neccessary to go and collect in the Bösnergarten or in a similar biotope at Regensburg. It is well known that of "Bryobia praetiosa" no $ $ are met. Only Ducès (1834) indicates males of his "Tetranychus cristatus”, and then only for those specimens found under stones at Paris in autumn. Moreover $ $ are regularly found of Bryobia sarothamni Geijskes 1939- I state that DuGès does not mention males for his specimens from the Midi on plum trees. So he must have collected more than one species, and as no specimens seem to have been preserved, we have to make a choice for the name ”cristatus” of DuGès. I should like to postpone this until I shall have had occasion to study the Bryobia from plum trees in Southern France and that living under stones in the public parks of Paris, for at all events we shall have to take a form which clearly shows the character chosen by Ducès for the name ”cristatus”, viz. the dorsum with a depressed centre surrounded by an elevated border (crista). With this Bryobia-problem we have to realize that as far as is known all forms or species, with the exception of B. sarothamni Geijskes and B. cristata (Dugès pro parte), show a thelytoke parthenogenesis. Now that the value of the biological observations can be confirmed by morphological differences, we have got the same situation as in various other zoological orders, so that in the present state of our knowledge there is no objection to describe the different forms as species. Transfer experiments have been made on various occasions in order to find a solution. I shall not mention them all. Some recent papers are those by Roosje & van Dinther (1952), Mathys (1954) and Böhm (1954), which all confirm once again that at least the great majority of such experiments will show a nega¬ tive result. In my opinion this fact is not strange at all. The fact that I have found constant morphological differences not only for the four groups as indicated by Mathys but also for various ’’species” in the field, seems to justify their publication, as it may be a help to other workers to know them. I am starting with two forms only of which I have seen a lot of material. Each future form will need a thorough study, as it is my intention to maintain the names of previous authors in all such cases where it will be possible and practical. When studying this genus I found that, apart from me, Mr. J. Meltzer, ’s-Graveland, had compared the morphological characters of Bryobia from ivy, apple and pear as well. He showed me his results which will be published in this same number of the Entomologische Berichten, and it is very satisfactory that they are entirely in accordance with my ideas, as is clearly appearing from his text and figures.
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